KR100198471B1 - Poisoning-resistant catalyst, process for production thereof, and process for using said catalyst - Google Patents

Abstract

The present invention is an endothelial toxic catalyst for the combustion of CO and combustion gas composed of an inorganic carrier, a noble metal active component supported on the inorganic carrier and silica supported on the noble metal active component, and a catalyst for combustible gas combustion in raw material addition using the catalyst. A combustion device is provided, wherein the active ingredient is composed of at least one selected from the group consisting of Pt, Rh, and Pd, wherein silica is more loaded on the surface of the catalyst, but gradually increases from the surface of the catalyst to the inner portion. It provides an endothelial toxicity catalyst characterized in that the precious metal active ingredient is further loaded. The catalyst has excellent endothelial toxicity and high activity at a low temperature of 200 ° C or less.

Description

Endothelial Toxic Catalyst, Preparation Method thereof, and Method of Using the Catalyst

1 is a schematic view showing the surface structure of the endothelial toxic catalyst of the present invention.

2 is a schematic diagram of a catalytic activity evaluation test apparatus.

3 is a graph showing the activity and endothelial toxicity of the catalyst according to an embodiment of the present invention.

4 is a graph showing the relationship between the Pt / Si (atomic ratio) of the catalyst and its initial activity and endothelial toxicity.

5 is a graph showing the relationship between the activity of the catalyst and the endothelial toxicity according to another embodiment of the present invention.

Figure 6 is a graph showing the activity and endothelial toxicity of the catalyst according to an embodiment of the present invention, in the case of H ₂ S of the toxic component.

7 is a graph showing the relationship between the primary firing temperature and the CO removal rate for the catalyst of the present invention.

8 is a graph showing the relationship between the primary firing temperature and the amount of residual chlorine for the catalyst of the present invention.

9 is a system flow diagram of a high purity nitrogen gas production apparatus that is an example of use of the endothelial toxicity catalyst of the present invention.

* Explanation of symbols for main parts of the drawings

1 Inorganic Carrier 2 Precious Metals

3: silica 4: thermocouple

5: catalyst 6: reaction tube

7: converted electric furnace 8: gas analyzer

10 adsorption separator 11 compressor

12 dust removal unit 13 catalyst tank

14 heater 15,18,21 conduit

16: heat exchanger 17: rectification tower

17 ': rectifier stage 19: deep cold separator

20: deep cold separation unit

The present invention relates to a catalyst for the combustion of flammable gases, and in particular, to remove flammable impurities (e.g., CO, H2, hydrocarbons, etc.) in source gas by catalytic combustion, and thus to endothelial toxicity used for purification of desired gases. It relates to a catalyst and a preparation method thereof.

Various gases are used in the production of semiconductor devices. In recent years, the demand for ultra-high purity gas is increasing for the purpose of improving the yield of products with the high integration and miniaturization of semiconductor devices. In particular, the ultra high purity is further required for the nitrogen gas used as the carrier gas or the atmosphere control gas, and the impurity tolerance in the nitrogen gas is also acceleratedly lowered.

In general, high-purity nitrogen gas is separated and collected by a deep cold separation of nitrogen gas from air, but a small amount of CO contained in the raw air cannot be removed by deep cold separation because the boiling point is close to nitrogen. Therefore, the catalyst is used to burn CO and then separated off before deep cooling.

As a method of purifying the desired gas by removing the combustible gas in the source gas by the catalytic combustion method, for example, Japanese Patent Application Publication No. Hei 3-7603, Japanese Patent Laid-Open No. 61-225568 and Japanese Utility Model Publication Digestion No. 61-123389. In these methods, was converted to a combustible gas, CO or H ₂ contained in the raw material gas to a CO ₂ or H ₂ O, respectively, by catalytic combustion, CO _2, or by using the adsorbing separator is installed on the downstream side of the catalytic combustor H ₂ Separation with O is carried out to the outside of the system, and raw material air from which CO or H ₂ is removed is separated by a deep cooling separator to produce a desired high purity gas.

As the catalyst used in the catalytic combustion method, noble metal catalysts such as PT and Pd having high activity in the low temperature region are usually used. However, when the source gas contains poisonous components of the catalyst (for example, SO ₂ or H ₂ S), these catalysts are poisoned and the activity is lowered. When the activity of the catalyst is lowered, the removal rate of the combustible gas in the source gas is lowered, so that the purity of the gas obtained by the deep cooling separator is lowered.

In order to solve this problem, the poisoning of the catalyst is prevented by providing a means for removing the poisonous component on the inlet side of the catalyst tank. For example, a method of removing SO ₂ gas, which is the main toxic component of the catalyst, has been proposed (Japanese Patent Laid-Open No. 2-119921). However, in the case of providing a means for removing the poisonous component of the catalyst, the production cost of the catalytic combustion device increases.

As another method for preventing catalyst poisoning, it is known to increase the reaction temperature of the catalyst tank. In other words, catalytic combustion at high temperature rather than catalytic combustion at low temperature is less likely to cause poisoning of the poisoned component in the catalyst, and therefore, deactivation of the catalyst can be suppressed. However, when the reaction rate is increased, the preheating of the source gas or the catalyst is required, which increases the operating cost.

An object of the present invention is to provide a combustion catalyst having a high activity and high endothelial toxicity at a low temperature, a method for producing the same, and a combustion device using the combustion catalyst.

Another object of the present invention is to provide a method of using the catalyst.

In order to achieve the above object, the present inventors have conducted various researches and experiments to invent an endothelial toxic catalyst having a property that the catalyst itself hardly adsorbs the toxic component.

The present invention provides an endothelial toxic catalyst for combustion of CO and flammable gas composed of an inorganic carrier, a noble metal active component supported on the inorganic carrier and silica supported on the noble metal active component, and a catalytic combustion device using the catalyst. The active ingredient is composed of at least one selected from the group consisting of Pt, Ph and Pd, and the silica is more loaded on the surface of the catalyst, but the precious metal active ingredient is more loaded as it gets deeper from the surface of the catalyst to the inner part. .

More specifically, the present invention provides a poisonous catalyst which is characterized in that the amount of silica to Pt, Ph and / or Pd is 4 to 20 in an atomic ratio of Si to these Pt, Ph and / or Pd. do.

In addition, the present invention, at least one of the metal salts of Pt, Ph and Pd is carried on at least the surface layer of the inorganic carrier to perform the primary firing at 700 to 800 ℃, colloidal silica is supported on the fired article and then at 400 to 600 ℃ Provided is a method for preparing an endothelial toxic catalyst for combustion of CO and flammable gas, in which secondary firing is performed.

In addition, the present invention is composed of the combustion of the flammable impurity gas in the raw air by using a catalyst to remove the combustion products by adsorption, and the separation of high-purity nitrogen gas containing no flammable impurity gas from the raw air by deep cooling separation. In the method for producing high purity nitrogen gas, there is provided a method comprising using an endothelial toxic catalyst composed of an inorganic carrier, a noble metal active ingredient supported on the inorganic carrier and a silica supported on the precious metal active ingredient. The noble metal active ingredient is composed of at least one selected from the group consisting of Pt, Ph and Pd, and silica is more loaded on the surface of the catalyst, but the precious metal active ingredient is more rich as it is deeper from the surface of the catalyst to the inner part. Become.

The endothelial toxic catalyst of the present invention can be used as a combustion catalyst, for example, for treating exhaust gas from a combustor, for treating exhaust gas from a heating device, and for treating exhaust gas from an incinerator.

As described above, the endothelial toxic catalyst of the present invention comprises an inorganic carrier (1), at least one precious metal (2) such as Pt, Pd or Ph, which is an active component supported on the inorganic carrier, as shown in the schematic diagram of the surface structure of FIG. It is a component which suppresses the adsorption of a toxic component and consists of silica (3) supported on a noble metal. At the surface of the catalyst, silica is more abundant than the noble metal active component, and as the depth deepens from the surface of the catalyst to the inner portion, the noble metal active component is more loaded than silica.

The amount of the precious metal supported on the endothelial toxicity catalyst of the present invention and the amount of silica supported on the precious metal is preferably in the range of 4 to 20 in terms of the atomic ratio of Si to the precious metal. When this ratio is less than 4, the endothelial toxicity is insufficient, and when this ratio exceeds 20, the activity of the catalyst decreases.

In order to make the endothelial toxic catalyst of the present invention have a structure as shown in the schematic diagram of FIG. 1, the metal salt solution or suspension of the noble metal is supported by impregnation with an inorganic carrier, and subjected to primary firing at high temperature (for example, 700 ° C). After performing the above step, the fired article may be impregnated with silica having a predetermined temperature (for example, colloidal silica), and then secondary firing may be performed on the impregnated article.

For catalytic activity, the primary firing temperature is preferably 700 to 800 ° C, and the secondary firing temperature is preferably 400 to 600 ° C. It was confirmed by scanning electron microscopy that the catalyst of the present invention had a structure as shown in the first schematic diagram. TiO ₂ , V ₂ O _5, and the like have been studied as inorganic compounds other than silica that suppress the adsorption of the toxic component to the catalyst. The results showed that V ₂ O ₅ was somewhat effective but degraded compared to silica, and moreover, it was found to be superior to the compound because silica is much cheaper and also non-toxic in itself.

Metal salts of noble metals (Pt, Pd, or Ph) include platinum chloride, dinitrodiamine platinum, tetrachloride chloride, platinum, palladium nitrate, palladium chloride, tetraamine palladium chloride, rhodium chloride, rhodium chloride hexaaminerhodium, rhodium sulfate, etc. This is used.

As silica, colloidal silica is preferable.

As the inorganic carrier, a porous inorganic carrier is preferable. As the porous inorganic material, alumina, silica, zirconia, mullite, cordierite and the like are used. The shape of the inorganic carrier can be arbitrarily selected according to the purpose, such as particulate type, pellet type, plate type, honeycomb structure, or the like.

The catalyst of the present invention is used as a catalyst for combustion of flammable gas in air. In particular, the catalyst of the present invention is used in an N ₂ production apparatus for producing N ₂ gas by a deep cold separation apparatus using air as a raw material. By using the catalyst, there is no need to provide a separate means for removing the toxic components, thereby simplifying the whole apparatus. Moreover, since the reaction temperature of the catalyst does not need to be made high in order to suppress adsorption of the toxic component, the operating cost can be reduced.

The endothelial toxic catalyst of the present invention has a sufficiently high activity in the low temperature range (75 to 200 ℃), it can achieve the above object.

When the endothelial toxicity of a catalyst in which only a noble metal is supported as an active ingredient is tested using a SO ₂ -containing gas, the catalyst is affected by SO ₂ , which is a poisonous component, and the metal is deteriorated. This is because the noble metal catalyst adsorbs SO ₂ and the catalytic activity is lowered.

On the other hand, the catalyst of the present invention has a high endothelial toxicity, as shown in FIG. 1, in order to apply a noble metal catalyst (for example, the active ingredient supported on the inorganic carrier), the supported silica may not adsorb the poisonous component. It is because it suppresses.

In the endothelial toxicity catalyst, the amount of silica added to the noble metal affects endothelial toxicity. This is because the noble metal catalyst cannot be sufficiently coated with silica when the atomic ratio of Si to noble metal is less than four. Moreover, when atomic ratio exceeds 20, there exists a tendency for initial activity to fall. It is considered that the reason for the decrease in the initial activity is that the precious metal catalyst is coated with too much silica, so that the number of active active sites is reduced and the effect as a catalyst is reduced.

Therefore, the amount of silica to obtain a catalyst having excellent endothelial toxicity and high initial activity is preferably 4 to 20 in terms of the atomic ratio of Si to the noble metal.

Next, an Example demonstrates this invention concretely.

Example 1 and Comparative Example 1

Γ-alumina (11 mm x 11 mm x 32 mm) having a honeycomb structure was used as the inorganic carrier, and Pt was selected as a catalyst. Platinum chloride solution was used as a raw material of Pt. The solution was diluted with midstream water until a predetermined concentration of Pt was reached so that a predetermined value of Pt content of the carrier was reached, taking into account the relationship between the water absorption of the carrier and the concentration of Pt (% by weight) in the chloroplatinic acid solution. The carrier thus prepared was immersed for 15 minutes by immersion. The excess solution adhering to the carrier was removed and first calcined in air at 700 ° C. for 2 hours.

At this time, the amount of Pt supported on the carrier was 1% by weight.

Next, the obtained primary calcined article was impregnated using a colloidal silica solution so that the atomic ratio of the second component Si to the first component Pt was 5, followed by secondary firing in air at 500 ° C. for 2 hours. A complete catalyst was obtained.

The primary fired article as described above was used as a comparative catalyst (a) and compared with the finished catalyst (b) in the active surface. Model gas, using a raw material gas mixed with a flammable gas of CO gas (N ₂ balance) in air was compared to CO removal.

2 shows an outline of the catalytic activity evaluation test apparatus.

A gas prepared by mixing an appropriate amount of CO gas into air is passed into the reaction tube 6 having the catalyst 5 having the honeycomb structure with a thermocouple 4 attached to the center thereof, and the reaction tube 6 is converted into a ring. The gas coming out of the reaction tube 6 during the heating in the electric furnace 7 was measured with a gas analyzer 8 to measure the CO concentration in the gas. The CO removal rate in the feed gas with respect to the reaction temperature was calculated by the following equation.

CO removal rate (%) = [(A-B) / A] × 100 [1]

In the above formula, A is the CO concentration in the source gas at the reaction tube inlet, and B is the CO concentration in the source gas at the outlet of the reaction tube.

The test conditions were as follows. The CO concentration in the source gas was 80 ppm (residual air), the space velocity (sv) was 30,000 h, the temperature was 125 ° C, and the pressure was atmospheric pressure.

In addition, the endothelial toxicity evaluation of the catalyst was carried out by mixing SO ₂ gas as a toxic component in the source gas and comparing the CO removal rate before and after the flow of the SO ₂ mixed gas. The concentration of SO ₂ gas in the source gas was adjusted to 30 ppm.

3 shows the activity and endothelial toxicity of each catalyst. As shown in FIG. 3, the initial activity before distribution of the SO ₂ gas was at a high level almost equal to those of the catalysts (a) and (b). However, when the SO ₂ mixed gas was passed through, the catalyst (A) was poisoned by SO ₂ and the activity was lowered, so the CO removal rate was reduced to 55% (after 5 hours). On the other hand, the CO removal rate of catalyst (b) is 82%, indicating very high endothelial toxicity.

Next, the SO ₂ adsorption amount of the catalysts (a) and (b) was measured. The SO ₂ adsorption amount was measured by circulating pulses of SO ₂ gas (He residue) under heating at 125 ° C.

As a result, the SO ₂ adsorption amount of the catalyst (a) was about 8.5 ml / g, while the SO ₂ adsorption amount of the catalyst (b) was as small as 3.5 ml / g. This fact shows that catalyst (b) has excellent endothelial toxicity.

In the same manner as described above, the CO removal rate of the catalyst was measured using V ₂ O ₅ or TiO ₂ instead of silica as the endotoxin (second component).

These catalysts were named as catalysts (c) and (d), respectively, and the measurement results are shown in FIG. Catalyst (c) was prepared in the same manner as catalyst (b) except that ammonium vanadate (NH ₄ VO ₃ ) was used to prepare the comparative catalyst (a) as described above. Catalyst (d) was prepared in the same manner as catalyst (b), except that titania sol was used to prepare comparative catalyst (a) as described above.

Example 2

A catalyst was prepared by varying the amount of silica supported on the same primary firing article (containing supported Pt catalyst) as described in Example 1. The relationship between atomic ratio of Si to Pt and endothelial toxicity was investigated. Endothelial toxicity evaluation was performed as described in Example 1. Distribution of SO ₂ gas mixture was evaluated by CO removal and after 4 hours. Test conditions were the same as in Example 1.

In FIG. 4, the Pt / Si atomic ratio was changed to indicate the endothelial toxicity after 4 hours of initial activity level and SO ₂ mixed gas distribution as CO removal rate.

It can be seen from FIG. 4 that the initial activity decreases when the amount of Si exceeds 20 (atomic ratio). It is also found that when the amount of Si is less than 4 (atomic ratio), the CO removal rate is equivalent to the CO removal rate of the catalyst (a) containing only Pt. However, even when Si amount is 20 (atomic ratio) or more, endothelial toxicity does not fall. These facts indicate that it is desirable to satisfy both endothelial toxicity and initial activity when the atomic ratio of Si to Pt is in the range of 4 to 20.

Example 3 and Comparative Example 2

As a carrier,? -Alumina (11 mm x 11 mm x 32 mm) having the same honeycomb structure as in Example 1 was used, and Pd was selected as a catalyst. A primary fired article was prepared in the same manner as described in Example 1 using a palladium nitrate solution as a raw material for Pd. The amount of Pd supported was 1.0% by weight. Thereafter, the primary calcined article was impregnated into the colloidal silica solution in the same manner as described in Example 1, and then secondary calcined in air at 500 ° C. for 2 hours to obtain a finished catalyst.

The primary fired article as described above was used as a comparative catalyst (e) and compared with the finished catalyst (f) in terms of activity. The amount of Si in the catalyst (f) was adjusted so that the atomic ratio of Si to Pd was adjusted by adjusting the concentration of the colloidal silica solution.

Figure 5 shows the results of evaluation of the activity and endothelial toxicity of the catalysts (e) and (f). In this case, the same measurement method as in Example 1 was used. In the case of Pd, the same results as those obtained for the Pt catalyst were obtained.

Example 4

Initial activity and endothelial toxicity of catalysts (a) and (b) prepared in Example 1 were evaluated using H ₂ S as the toxic component gas. The H ₂ S concentration in the source gas was adjusted to 30 ppm, and the comparative test was carried out under the same conditions as described in Example 1. 6 shows the activity and endothelial toxicity of the catalysts (a) and (b). As shown in FIG. 6, both catalysts have the same activity as Example 1 in the initial activity before H ₂ S flows.

However, when the toxic component H ₂ S is mixed into the source gas and distributed, the comparative catalyst (a) containing only Pt alone is poisoned by H ₂ S and the activity is drastically reduced.

On the other hand, the supported silica-containing catalyst (b) has excellent endothelial toxicity, and it can be seen that there is no particular change in endothelial toxicity even when H ₂ S is present instead of SO ₂ as the poisonous component.

Example 5

Except for changing the primary firing temperature, the catalyst of the present invention prepared in the same manner as in Example 1 compared the CO removal rate. The results are shown in FIG. Secondary baking conditions were 500 degreeC and 2 hours.

As shown in FIG. 7, the primary firing temperature is preferably 700 to 800 ° C.

As can be seen from FIG. 8, it is estimated that the primary firing temperature is related to the amount of residual chlorine in the catalyst, and that if the chlorine content is adjusted to 0.1% by weight or less, it is possible to obtain a catalyst having the same catalytic activity. Can be.

In addition, similarly to the primary firing temperature, when the secondary firing temperature is examined, it is found that 400 to 600 ° C is preferable.

Moreover, it becomes clear from FIG. 7 that the catalyst of the present invention can obtain sufficient catalysis even at a reaction temperature as low as 75 ° C.

Example 6

9 shows a system flow diagram of an apparatus for producing high purity nitrogen gas, which is an example of use of the endothelial toxic catalyst of the present invention.

Through the dust removal unit 12, the raw material air G ₁ pressurized by the compressor 11 is supplied to the catalyst tank 13 until it reaches a predetermined pressure. It is the inlet side of the heater 14 of the catalyst tank 13 is installed, to heat the feed air G ₁ at a predetermined temperature. The heater 14 can control the raw air G ₁ to be a temperature in the reaction temperature range (75 to 200 ° C) of the catalyst.

The catalyst tank 13 is filled with an endothelial toxic catalyst (not shown) having a honeycomb structure.

The raw air G ₁ preheated in the heater 14 flows into the catalyst tank 13.

In the catalyst tank 13, combustible gas components such as CO or H ₂ contained in the source gas G ₁ are combusted to convert CO into CO ₂ and H ₂ into H ₂ O. The gas containing such a combustion product (hereinafter referred to as raw material gas G ₂ ) is transferred to the adsorption separator 10 installed at the outlet side of the catalyst tank 13 so that impurities such as CO ₂ or H ₂ O are adsorbed and removed. . Gases from which CO ₂ and H ₂ O have been removed (hereinafter, referred to as raw material air G ₃ ) are supplied to the deep cooling separator device 20 through the conduit 15.

The deep cold separator unit 20 is composed of main parts such as the deep cold separator 19, the heat exchanger 16, the rectification tower 17, and the like. First, the raw material air G ₃ is introduced into the heat exchanger 16. In the heat exchanger 16, the raw material air G ₃ is cooled by heat exchange with N ₂ of low temperature separated in advance.

The cooled raw air G ₃ is then supplied to the bottom of the rectification tower 17 via conduits 18. In the lower part, the raw air G ₃ is rectified and separated by gas-liquid contact with the liquid of the plurality of rectifying stages 17 'installed in the rectifying tower 17. N ₂ gas is discharged through the conduit at the top of the rectification tower 17 and the product N ₂ gas is discharged through the conduit 21.

When the product N ₂ gas is sent as described above, the troublesome separation gas such as CO or H ₂ contained in the raw material air is removed by catalytic combustion in the previous stage of rectification operation, so that the product N ₂ gas is CO, H ₂ It is a high purity N ₂ gas containing no impurities, such as. In particular, when the endothelial toxic catalyst of the present invention is used in the catalyst tank, even if the toxic component (SO ₂ , H ₂ S, etc.) is contained in the raw air, the catalyst is less deteriorated, and thus the removal rate of the flammable gas is not lowered. Therefore, high purity N ₂ gas can be produced stably.

Claims (7)

A catalytic combustion apparatus for combusting flammable gas in raw air by catalytic combustion, comprising: an inorganic carrier, a noble metal active component supported on the inorganic carrier, and a silica supported on the noble metal active component for the combustion of CO and flammable gas Composed of at least one selected from the group consisting of Pt, Rh and Pd, wherein the catalyst is present in the catalytic combustion device, and silica is more loaded on the surface of the catalyst. Improved catalytic combustion apparatus, characterized in that the noble metal active ingredient is more loaded as the deeper from the surface of the catalyst to the inner portion. In the endothelial toxic catalyst for combustion of CO and combustible gases composed of an inorganic carrier, a noble metal active component supported on the inorganic carrier and silica supported on the noble metal active component, the noble metal active component is selected from the group consisting of Pt, Rh and Pd. And at least one selected from the group consisting of more silica on the surface of the catalyst, but more noble metal active ingredient is further loaded from the surface of the catalyst into the inner portion. The endothelial catalyst according to claim 2, wherein the amount of silica to Pt, Rh and / or Pd is 4 to 20 in an atomic ratio of Si to Pt, Rh and / or Pd. The endothelial toxicity catalyst according to claim 2 or 3, wherein alumina having a honeycomb structure is used as the inorganic carrier. At least one of the metal salts of Pt, Rh and Pd is supported on at least the surface layer of the inorganic carrier, subjected to primary firing at 700 to 800 ° C., and then to colloidal silica on the fired article, and then secondary firing at 400 to 600 ° C. Endothelial toxicity catalyst, characterized in that for producing CO and combustible gas combustion. 6. The endothelium of claim 5, wherein the colloidal silica has a concentration of 4 to 20 in terms of the atomic ratio of Si to Pt, Rh and / or Pd. Toxic catalyst. The endothelial toxicity catalyst according to claim 5 or 6, wherein? -Alumina having a honeycomb structure is used as the inorganic carrier.